* This removes a bunch of unsupported functionality that is provided
in InheritedViews.
* Speeds up action rendering because we don't have to wait for an
exception to be raised on each action.
* Brings rendering logic into Active Admin which will make it easier for
the upgrade to Rails 3.1
* Reduces the number of dependencies... which is always good.

* Removed ActiveAdmin.admin_notes from the default initializer. The
option is no longer used.
* Added a comment oon ActiveAdmin.admin_notes that its deprecated, but
we should probably add a deprecation notice so that users can remove
it from their initializer.
* Added a comment about ActiveAdmin.allow_comments_in which is the new
option for turning on and off comments in a namespace.
* Closes #73